1. Field of the Invention
The present invention relates to a rotational angle detecting device which is capable of detecting abnormality of an angle sensor (whether or not short-circuit between output terminals of the angle sensor occurs) detecting a rotational angle of a rotary element.
2. The Related Art of the Invention
FIG. 5 shows a conventional device for detecting a rotational angle of a rotary element.
This device is arranged in such a manner that a first angle sensor 100 and a second angle sensor 200 are located as opposed to a rotary element (not shown). Output wave profiles outputted in accordance with rotation of the rotary element from the first angle sensor 100 and the second angle sensor 200 are respectively amplified by a first signal amplifier 101 and a second signal amplifier 201 and thereafter, a calculating section 300 detects a rotational angle of the rotary element based upon a signal (Vo1) outputted from the first signal amplifier 101 and a signal (Vo2) outputted from the second signal amplifier 201.
Here, the first angle sensor 100 and the second angle sensor 200 are arranged to deviate from each other by 90 degrees. This arrangement, as shown in FIG. 6, causes the signal Vo1 and the signal Vo2 to be inputted to the calculating section 300 in the form that the wave profile of the signal Vo1 and the wave profile of the signal Vo2 deviate in phase by 90 degrees from each other.
In addition, the calculating section 300 calculates a difference amount between the signal Vo1 and the signal Vo2 outputted from the first signal amplifier 101 and the second signal amplifier 201 to determine whether or not the calculated difference amount is beyond a predetermined value. The calculating section 300 is, based upon the determination result, detects whether or not an abnormality such as a break or a short-circuit occurs in a wire 105 (wire by which the signal Vo1 is transmitted) connecting between the first signal amplifier 101 and the calculating section 300.
For example, JP-9-178512A discloses an arrangement of thus detecting abnormality of a device by comparing signals outputted from two angle sensors.
In the conventional rotational angle detecting device, an abnormality of the wire 105 connecting between the first signal amplifier 101 and the calculating section 300 can be detected. However, in a case where a short-circuit between an output terminal 102 of the first angle sensor 100 and an output terminal 202 of the second angle sensor 200, a short-circuit between the output terminals 102 and 103 of the first angle sensor 100 or further a short-circuit between the output terminals 202 and 203 of the second angle sensor 200 occurs, the short-circuit thereof can not be detected. For example, in a case where the output terminal 102 of the first angle sensor 100 and the output terminal 202 of the second angle sensor 200 are short-circuited, a signal Vo1′ and a signal Vo2′ outputted from the first signal amplifier 101 and the second signal amplifier 201, as shown in FIG. 6, deviate in amplitude and phase from a signal Vo1 and a signal Vo2 in a normal state of the device.
As shown in FIG. 6, however, a voltage of each of the signals Vo1 and Vo2 in a normal state of the angle sensor and a voltage of each of the signals Vo1′ and Vo2′ at an abnormal state thereof are all equal in the vicinity of, for example, 45 degrees and 225 degrees in angle of the rotary element. In consequence, in the vicinity of these angles the abnormality such as breaking or short-circuit of the output terminals 102, 103, 202, and 203 can not be detected simply by comparing the signals Vo1′ and Vo2′. Further, since it is not until the signals Vo1 and Vo2 change that the normality or the abnormality of the angle sensor can be determined, the normality or the abnormality of the angle sensor can not be determined until the rotary element starts to rotate.
In addition, there exists a characteristic variation in an element used in each of the first angle sensor 100 and the second angle sensor 200. Therefore, when the signals Vo1 and Vo2 are close to the signals Vo1′ and Vo2′, the rotational angle detecting device errs in detecting an occurrence of an abnormality such as a break or a short-circuit in the wire by comparing the signals Vo1 and Vo2.
In view of the above, there exists a need for a rotational angle detecting device which overcomes the above-mentioned problems in the related art. The present invention addresses this need in the related art as well as other needs, which will become apparent to those skilled in the art from this disclosure.